The clippings of grass, leaves and other organic waste material generated by a rotary lawn mower offer a problem to proper lawn maintenance. If simply left on a lawn, such materials will often dry and form an unsightly mat over the top of a lawn which can harm the grass below by not allowing sunlight to penetrate. Alternatively, such materials will often fall between the blades of grass. If such clippings are relatively large, they will not readily decay but instead will form a mat along the ground surface, virtually choking and destroying the lawn.
Typically, such clippings are collected by use of a lawn mower attachment. The use of such an attachment necessitates that the mower be stopped and the clippings be emptied either during or at the end of the mowing process. Alternatively, the clippings may be removed by raking. Similar to emptying clippings from a lawn mower attachment, this involves extra work. Furthermore, whether the clippings are collected via an attachment or by raking, the gardener is left with the additional problem of disposing of such clippings.
Due to environmental concerns, it is becoming less desirable to dispose of such clippings in the traditional manner, i.e., by bagging them in plastic containers and allowing them to be carried off to a disposal facility such as a land fill or incinerator. While alternatively such materials may be composted, that requires a fairly large amount of space and tends to be malodorous. Because of these drawbacks, composting is especially undesirable in a typical urban environment.
If cut in fine pieces, clippings may be allowed to remain in a lawn with beneficial results. Such finely cut clippings will not form a mat over the top of the lawn, but instead will fall between the blades of grass. Because of the small size of such clippings, they will readily decompose providing nutrients to the lawn instead of forming a choking mat at the base of the blades of grass. Such finely cut clippings are generally referred to as "mulch" and the term "mulching" will be used to refer to a process or method by which such clippings are formed.
Mulching blades which may be used in lieu of traditional lawn mower cutting blades are already known in the art. U.S. Pat. Nos. 4,205,512; 4,292,791; 4,318,268; 4,617,788; 5,094,065; 5,197,268; and 5,209,052 all disclose such mulching blades.
Mulching blades which can be used in conjunction with the normal cutting blade of a rotary mower have also been proposed. U.S. Pat. No. 4,083,166, issued on Apr. 11, 1978 to Haas, discloses a mulching disk attachment which has a mounting hole such that the mulching attachment may be secured to the drive shaft of a rotary mower alongside, i.e., in a contacting relationship with, the cutting blade. The problem with this arrangement is that the efficiency of the cutting blade is reduced due to the operational loss of that portion of the cutting blade in a contacting relationship with the mulching attachment. The claimed mulching disk attachment in Haas also requires impeller blades extending upwardly from the disk for inducing a flow of air upwardly. While the lawn mower cutting blade alone usually induces such an air flow, because the mulching attachment disclosed in Haas is in a contacting relationship with the cutting blade, and interferes with the normal flow of air resulting therefrom, such impeller blades become necessary. The mulching attachment disclosed in Haas also has another drawback in that it requires the use of a separate flanged blade support member to secure and prevent rotation of the mulcher attachment relative to the drive shaft and cutting blade during use.
U.S. Pat. No. 4,967,546, issued on Nov. 6, 1992 to Forbush, discloses a mulching attachment comprising a disk-like base having a cylindrical blade assembly disposed around and attached to the periphery of the disk-like base. Fan vanes are also connected to the disk-like base and are designed to create a radial flow of air across the disk. A problem with the Forbush mulching attachment is that its construction is fairly complex due to the fan vanes and the blade assembly which must be attached to the disk-like base, making it more expensive and subject to component failure. Furthermore, in order to retrofit an existing lawn mower with the Forbush mulching attachment, a mounting collar is disclosed which utilizes a set screw to lock the mounting collar against the drive shaft of the mower. A problem with this arrangement is its lack of universality; a different mounting collar must be provided in order to mount the mulching attachment to different mower drive shafts. Another problem with the Forbush arrangement is that the cylindrical blade assembly requires space between the cutting blade and the lawn mower housing. If such space is not available, the Forbush mulching attachment cannot be used to retrofit that lawn mower.
None of the prior art mulching blade arrangements disclose a mulching blade which is not only easy to manufacture, but which may be easily secured to the drive shaft of a number of existing commercial rotary lawn mowers and which does not interfere with the normal function of the existing cutting blades of such lawn mowers.